This invention relates to a shut-off and regulating valve comprising a housing, a valve disk journaled in the housing, and a seat ring with which the valve disk can be brought into contact.
U.S. Pat. No. 3,968,699 discloses a shut-off valve which has a seat ring with a resilient gasket for normal operation and, in case of damage, especially in a fire, a sealing lip of metal. This metal sealing lip is a component of a seat holding ring with which the seat ring is held in a chamber of the housing. The sealing lip has, in the unloaded state, essentially the same alignment as in the case of a closed valve disk. In the previously known shut-off valve the metal sealing lip by no means suffices to satisfy requirements with regard to the needed sealing action between the sealing surface and the valve disk, and a comparatively high leakage is to be expected. For the proper operation of the shut-off valve in normal operation, the seat ring of resilient material is absolutely necessary, the radial bias being applied by means of an additional resilient ring in order to satisfy the stringent requirements as regards sealing tightness and minimum leakage. The difficulty of manufacturing the previously known shut-off valve is therefore substantial.
Furthermore, a check valve is disclosed in German Democratic Republic Patent No. 142,377, in which the valve disk is journaled in the housing with double eccentricity. In the housing a seat holding ring consisting of metal is fastened, which has a rounded seat surface for the valve disk. The rounded seat surface is a component of an annular internal portion of the seat ring, and the said internal portion is joined to the rest of the seat ring by a more or less radially aligned connecting piece. This connecting piece permits a certain elastic movement of the internal portion with the rounded contact surface when the valve disk is closed. The production of such a seat ring is very difficult because the manufacturing tolerances of various parts must be precisely coordinated with one another if sufficient sealing is to be possible. Also, when the seat ring is installed, the it must be precisely positioned with respect to the valve disk, and thereafter must be precisely secured in the housing by means of the additional seat holding ring. Such adjustment calls for the use of especially qualified personnel and involves appreciable cost. Finally, special measures must be taken to assure that the optimum positioning achieved with a certain probability during assembly will also be reliably maintained in the following period of operation. Even slight shifting of the seat ring due to the forces acting on it would have a very disadvantageous effect on the sealing and, in some cases, would call for quite difficult repairs.
Furthermore, Japanese patent application 63-210,472-A discloses a safety valve which, again, has a sealing ring for normal operation made from an elastomer or a comparable nonmetallic material having a tongue which is aligned substantially radially. By means of an additional spring ring a radial bias is achieved with respect to the outside surface of the valve disk. In case of a fire, the seat ring has an additional sealing lip of metal with which the valve disk comes in contact. As explained above, such a metal sealing lip cannot produce a sufficient sealing in normal operation to satisfy the leak-proof sealing requirements which then apply. This is because comparatively high surface pressures between the seat ring and the valve disk would have to be anticipated, and this can result in disadvantages in regard to the service life and the materials that are used. To enable the required seal to be achieved between the spherical sealing surface of the valve disk and the seat ring, relatively high torques would have to be applied to open and close the valve. The driving means for actuating the valve would therefore have to be constructed sufficiently sturdily.